Liquid crystal display apparatus and method of driving the liquid crystal display apparatus

Technical field

The present invention relates to a liquid crystal display apparatus. In particular, the present invention relates to a technology that suppresses an occurrence of color shift in a color-field sequential liquid crystal display apparatus.

Background art

In general, in liquid crystal display apparatuses that perform color display, one pixel is divided into three sub-pixels: a red pixel provided with a color filter that transmits red light, a green pixel provided with a color filter that transmits green light, and a blue pixel provided with a color filter that transmits blue light. Although the color filters provided in the three sub-pixels enable the color display, about two-thirds of backlight light with which the liquid crystal panels are irradiated are absorbed by the color filters. As a result, there is a problem in that the color filter type liquid crystal display apparatuses have low light use efficiency. Accordingly, color-field sequential liquid crystal display apparatuses that perform the color display without using the color filters attract attention.

In the common liquid crystal display apparatuses that adopt the field sequential method, one frame period during which one screen is displayed is divided into three fields. Although each field is also called a sub-frame, the term “field” is consistently used in the following description. For example, one frame period is divided into a field (red field) in which a red screen is displayed on the basis of red components of an input image signal, a field (green field) in which a green screen is displayed on the basis of green components of the input image signal, and a field (blue field) in which a blue screen is displayed on the basis of blue components of the input image signal. Displaying each primary color in the above manner causes a color image to be displayed in the liquid crystal panel. Since the color display is performed in the above manner, it is not necessary to provide the color filters in the color-field sequential liquid crystal display apparatuses. Accordingly, the light use efficiency of the color-field sequential liquid crystal display apparatuses is about three times higher than that of the color filter type liquid crystal display apparatuses. Consequently, the color-field sequential liquid crystal display apparatuses are appropriate for increase in luminance and reduction in power consumption.

In this description, a combination of the value of data about the red components, the value of data about the green components, and the value of data about the blue components is referred to as “an RGB combination.” For example, “R=128, G=32, and B=255” is an example of one RGB combination. In this example, the value of data about the red components has a value of 128, the value of data about the green components has a value of 32, and the value of data about the blue components has a value of 255. The value of data is typically a gradation value.

In the liquid crystal display apparatuses, image display is performed by controlling the transmittance of each pixel with voltage (liquid crystal applied voltage). It takes several milliseconds from a time when writing of data into each pixel (application of the voltage) is started to a time when the transmittance at the pixel reaches a target transmittance. Accordingly, in the color-field sequential liquid crystal display apparatuses, a backlight of the corresponding color is switched from a turned-off state to a turned-on state after the liquid crystal responds in each field to some extent.

In the liquid crystal display apparatuses, sufficient image quality may not be achieved, for example, in display of a movie due to a low response speed of the liquid crystal. Accordingly, a driving method called overdrive driving (overshoot driving) has hitherto been adopted as a countermeasure against the low response speed of the liquid crystal. The overdrive driving is a driving method in which drive voltage that is higher than predetermined gradation voltage corresponding to the value of data about the input image signal of the current frame or drive voltage that is lower than the predetermined gradation voltage corresponding to the value of data about the input image signal of the current frame is supplied to the liquid crystal panel depending on a combination of the value of data about the input image signal of the first previous frame and the value of data about the input image signal of the current frame. In other words, in the overdrive driving, compensation is performed so as to enhance the temporal change (not the special change) of the value of data for the input image signal. Adopting such overdrive driving causes the liquid crystal to respond so that the transmittance substantially reaches a target value (target transmittance) in each field in the current color filter type liquid crystal display apparatuses.

The following Patent Literatures in Citation List are known in association with the invention in this description. PTL 1 discloses an invention related to a compensation operation of color impurity in a color sequential LCD image display apparatus. According to this invention, a signal of each color is compensated on the basis of a signal of a preceding color. For example, when the colors are displayed in the order of “blue, green, and red”, the signal of green is compensated on the basis of the signal of blue. In addition, PTL 2 discloses an invention related to color reproducibility in a time-division color liquid crystal display apparatus. According to this invention, scanning timing of a time-division three-primary-color light emitting apparatus is delayed by an amount corresponding to an optical response speed of the liquid crystal and a non-light-emitting period corresponding to the optical response time of the liquid crystal is provided. In writing of data into each pixel, gamma correction is performed, which is based on a result of comparison between data about the previous field (the first previous field of the current field) and data about the current field. CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2003-502687

PTL 2: Japanese Unexamined Patent Application Publication No. 7-121138 SUMMARY OF INVENTION Technical Problem

As described above, in the current color filter type liquid crystal display apparatuses, the adoption of the overdrive driving causes the liquid crystal to respond so that the transmittance substantially reaches a target value in each field. Accordingly, the sufficient image quality is achieved. However, in the color-field sequential liquid crystal display apparatuses, the sufficient image quality is not achieved because of the following reasons even when the transmittance reaches a target value in each field through the overdrive driving. In the color-field sequential liquid crystal display apparatuses, although the backlight is switched from the turned-off state to the turned-on state during each field, as described above, the transmittance has not reached the target value at the start of the turning on of the backlight. Accordingly, the liquid crystal state (the state of orientation of liquid crystal molecules) is varied also during the turning on of the backlight. Consequently, one-to-one correspondence is not established between the liquid crystal state at the end of each field and the luminance actually displayed in each field (display luminance). As a result, it is not possible to preferably control the color balance (chromaticity) which is desirably displayed in each field in the overdrive driving in related art, thereby causing the color shift. As described above, in the color-field sequential liquid crystal display apparatuses, the sufficient image quality is not achieved even when the transmittance reaches a target value in each field through the overdrive driving.

A case will now be considered in which a color of an RGB combination “R=128, G=128, and B=32” is displayed in a liquid crystal display apparatus using gradation data in which each color has eight bits. Referring to FIG. 35 to FIG. 37 , a period during which a red backlight is turned on is denoted by TR, a period during which a green backlight is turned on is denoted by TG, and a period during which a blue backlight is turned on is denoted by TB. Variation in liquid crystal state is represented by variation in gradation value in FIG. 35 to FIG. 37 .

If the liquid crystal molecules have ideal response characteristics, that is, if the response time of the liquid crystal when the field is switched is constantly zero, the liquid crystal state is varied in a manner illustrated by a bold line 91 in FIG. 35 even when the overdrive driving is not adopted. At this time, the RGB combination of a display gradation value is “R=128, G=128, and B=32.” However, the response time of the liquid crystal is not actually zero. Accordingly, when the overdrive driving is not adopted, the liquid crystal state is varied in a manner illustrated by a bold line 92 in FIG. 36 . At this time, the RGB combination of an attained gradation value at the end of the red field, the green field, and the blue field is, for example, “R=102, G=120, and B=65.” As described above, when the overdrive driving is not adopted, a desired attained gradation value is not achieved at the end of the respective fields. Since the liquid crystal state is varied also during the turning on of the backlight, the RGB combination of the display gradation value is, for example, “R=90, G=114, and B=81.”

When the overdrive driving is adopted, the liquid crystal state is varied in a manner, for example, illustrated by a bold line 93 in FIG. 37 . At this time, the RGB combination of the attained gradation value at the end of the red field, the green field, and the blue field is “R=128, G=128, and B=32.” The liquid crystal responds in the above manner so as to achieve the desired attained gradation value at the end of the respective fields. However, since the liquid crystal state is varied also during the turning on of the backlight, as described above, a desired display luminance is not achieved. The RGB combination of the display gradation value is, for example, “R=99, G=128, and B=60.” The color shift occurs in the above manner in the color-field sequential liquid crystal display apparatus even when the overdrive driving is adopted.

In order to resolve the above problems, an object of the present invention is to realize a color-field sequential liquid crystal display apparatus capable of suppressing an occurrence of the color shift. Solution to Problem

In a first aspect, the present invention provides a color-field sequential liquid crystal display apparatus that divides one frame period into a plurality of fields and displays different colors in different fields to perform color display. The color-field sequential liquid crystal display apparatus includes a liquid crystal panel on which an image is displayed; a backlight that irradiates the liquid crystal panel with light; an input image data separation unit that separates input image data into input gradation data for every field; a data compensation unit that determines applied gradation data, which corresponds to voltage to be applied to the liquid crystal panel, by compensating the input image data while acquiring liquid crystal state data, which corresponds to expected attained gradation at the end of each field; a liquid crystal panel driving unit that drives the liquid crystal panel on the basis of the applied gradation data; and a backlight driving unit that drives the backlight so that the liquid crystal panel is irradiated with light of different colors in different fields. The data compensation unit includes a liquid-crystal state data acquirer that acquires the liquid crystal state data about a current field on the basis of the input gradation data about the current field and the liquid crystal state data about a first previous field of the current field and that is provided for each field composing one frame period; and an applied gradation data determiner that determines the applied gradation data about the current field by compensating the input gradation data about the current field on the basis of the liquid crystal state data about the first previous field of the current field and that is provided for each field composing one frame period. The applied gradation data determiner determines the applied gradation data so that a display luminance in each field is a display luminance corresponding to the input gradation data resulting from the separation by the input image data separation unit. The provision of the liquid-crystal state data acquirer and the applied gradation data determiner for every field composing one frame period allows the applied gradation data about an arbitrary displayed field to be determined by acquiring the liquid crystal state data about a first previous field of the displayed field on the basis of the input gradation data about the first previous field of the displayed field and the liquid crystal state data about a second previous field of the displayed field and compensating the input gradation data about the displayed field on the basis of the acquired liquid crystal state data.

In a second aspect of the present invention, in the first aspect, the data compensation unit includes a field memory that is capable of holding data corresponding to one field; one frame period is divided into P-number fields, in which P is an integer larger than or equal to three; the liquid crystal state data about a P-th field is held in the field memory; the liquid-crystal state data acquirer for a first field acquires the liquid crystal state data about the first field of a current frame on the basis of the input gradation data about the first field of the current frame and the liquid crystal state data about the P-th field of a previous frame, which is held in the field memory; the applied gradation data determiner for the first field determines the applied gradation data about the first field of the current frame by compensating the input gradation data about the first field of the current frame on the basis of the liquid crystal state data about the P-th field of the previous frame, which is held in the field memory; the liquid-crystal state data acquirer for a Q-th field, in which Q is an integer larger than or equal to two and smaller than or equal to P, acquires the liquid crystal state data about the Q-th field of the current frame on the basis of the input gradation data about the Q-th field of the current frame and the liquid crystal state data about a (Q−1)-th field of the current frame; and the applied gradation data determiner for the Q-th field determines the applied gradation data about the Q-th field of the current frame by compensating the input gradation data about the Q-th field of the current frame on the basis of the liquid crystal state data about the (Q−1)-th field of the current frame.

In a third aspect of the present invention, in the first aspect, the color-field sequential liquid crystal display apparatus further includes a data conversion unit that divides the area of the liquid crystal panel into a plurality of subareas to determine a light emitting luminance of the backlight corresponding to each subarea on the basis of the input gradation data about each pixel included in each subarea and that converts the input gradation data resulting from the separation by the input image data separation unit on the basis of the light emitting luminance. Converted input gradation data converted by the data conversion unit is supplied to the data compensation unit as the input gradation data. The backlight driving unit drives the backlight so that the backlight corresponding to each subarea emits light on the basis of the light emitting luminance determined by the data compensation unit.

In a fourth aspect of the present invention, in the first aspect, the liquid-crystal state data acquirer includes a liquid-crystal state data acquisition lookup table in which values associated with the input gradation data about the current field, values associated with the liquid crystal state data about the first previous field of the current field, and values corresponding to combinations of the values associated with the input gradation data about the current field and the values associated with the liquid crystal state data about the first previous field of the current field are stored; the liquid crystal state data about the current field is acquired on the basis of the liquid-crystal state data acquisition lookup table; the applied gradation data determiner includes an applied gradation data determination lookup table in which values associated with the input gradation data about the current field, values associated with the liquid crystal state data about the first previous field of the current field, and values corresponding to combinations of the values associated with the input gradation data about the current field and the values associated with the liquid crystal state data about the first previous field of the current field are stored; and the applied gradation data about the current field is acquired on the basis of the applied gradation data determination lookup table.

In a fifth aspect of the present invention, in the first aspect, one frame period is divided into three fields including a red field in which a red screen is displayed, a green field in which a green screen is displayed, and a blue field in which a blue screen is displayed.

In a sixth aspect of the present invention, in the first aspect, one frame period is divided into four fields including a white field in which a white screen is displayed, a red field in which a red screen is displayed, a green field in which a green screen is displayed, and a blue field in which a blue screen is displayed.

In a seventh aspect of the present invention, in the first aspect, one frame period is divided into at least three fields each capable of display of a mixed color screen, and screens of different colors are displayed in the at least three fields.

In an eighth aspect of the present invention, in the first aspect, the liquid crystal panel includes a pixel electrode arranged in a matrix pattern; a common electrode arranged so as to be opposed to the pixel electrode; a liquid crystal sandwiched between the pixel electrode and the common electrode; a scanning signal line; a video signal line to which a video signal corresponding to the applied gradation data is applied; and a thin film transistor a control terminal of which is connected to the scanning signal line, a first conductive terminal of which is connected to the video signal line, a second conductive terminal of which is connected to the pixel electrode, and a channel layer of which is formed of oxide semiconductor.

In a ninth aspect of the present invention, in the eighth aspect, the oxide semiconductor contains indium (In), gallium (Ga), zinc (Zn), and oxygen (O) as major components.

In a tenth aspect, the present invention provides a method of driving a color-field sequential liquid crystal display apparatus that includes a liquid crystal panel on which an image is displayed and a backlight that irradiates the liquid crystal panel with light and that divides one frame period into a plurality of fields and displays different colors in different fields to perform color display. The method includes an input image data separating step of separating input image data into input gradation data for every field; a data compensating step of determining applied gradation data, which corresponds to voltage to be applied to the liquid crystal panel, by compensating the input image data while acquiring liquid crystal state data, which corresponds to expected attained gradation at the end of each field; a liquid crystal panel driving step of driving the liquid crystal panel on the basis of the applied gradation data; and a backlight driving step of driving the backlight so that the liquid crystal panel is irradiated with light of different colors in different fields. The data compensating step includes a liquid-crystal state data acquiring step of acquiring the liquid crystal state data about a current field on the basis of the input gradation data about the current field and the liquid crystal state data about a first previous field of the current field; and an applied gradation data determining step of determining the applied gradation data about the current field by compensating the input gradation data about the current field on the basis of the liquid crystal state data about the first previous field of the current field. The applied gradation data determining step determines the applied gradation data so that a display luminance in each field is a display luminance corresponding to the input gradation data acquired in the input image data separating step. The applied gradation data about an arbitrary displayed field is determined by acquiring the liquid crystal state data about a first previous field of the displayed field on the basis of the input gradation data about the first previous field of the displayed field and the liquid crystal state data about a second previous field of the displayed field and compensating the input gradation data about the displayed field on the basis of the acquired liquid crystal state data. Advantageous Effects of Invention

According to the first aspect of the present invention, the color-field sequential liquid crystal display apparatus includes the liquid-crystal state data acquirer, which acquires the liquid-crystal state data about the current field on the basis of the input gradation data about the current field and the liquid-crystal state data (data corresponding to expected attained gradation at the end of the previous field) about the previous field (the first previous field of the current field), and the applied gradation data determiner, which determines the applied gradation data about the current field by compensating the input gradation data about the current field on the basis of the liquid-crystal state data about the previous field. Accordingly, it is possible to perform the compensation to enhance the temporal change of the values of data for the input image data so that the integral value of the luminance values during the turning on of the backlight reaches a target display luminance in consideration of the change in the liquid crystal state in all the previous fields. Consequently, even when the liquid crystal state is varied during the turning on of the backlight, a desired display luminance is achieved in each field. As described above, the color-field sequential liquid crystal display apparatus is realized, which is capable of suppressing an occurrence of the color shift.

According to the second aspect of the present invention, advantages similar to those in the first aspect of the present invention are reliably achieved.

According to the third aspect of the present invention, the liquid crystal display apparatus includes the data conversion unit that performs the so-called local dimming. Accordingly, the color-field sequential liquid crystal display apparatus is realized, which is capable of reducing the power consumption of the backlight while suppressing an occurrence of the color shift.

According to the fourth aspect of the present invention, even when many kinds of the liquid crystal panels exist, it is sufficient to change the values in the lookup tables (the liquid-crystal state data acquisition lookup table and the applied gradation data determination lookup table) depending on response characteristics of each liquid crystal panel.

According to the fifth aspect of the present invention, advantages similar to those in the first aspect of the present invention are achieved in the color-field sequential liquid crystal display apparatus adopting the common configuration of one frame period.

According to the sixth aspect of the present invention, one frame period is composed of the white field, the red field, the green field, and the blue field. In other words, one frame period includes a field for display of a color mixture component of at least two colors of the three primary colors, in addition to the three fields. In each of the three fields, the single color display of each color in the three primary colors is performed. Accordingly, an occurrence of the color breakup is suppressed. As described above, the color-field sequential liquid crystal display apparatus is realized, which is capable of suppressing an occurrence of the color breakup and suppressing an occurrence of the color shift.

According to the seventh aspect of the present invention, one frame period is composed of at least three fields each capable of display of a mixed color screen. Accordingly, as in the sixth aspect of the present invention, the color-field sequential liquid crystal display apparatus is realized, which is capable of suppressing an occurrence of the color breakup and suppressing an occurrence of the color shift.

According to the eighth aspect of the present invention, in the color-field sequential liquid crystal display apparatus, the thin film transistor the channel layer of which is formed of oxide semiconductor is used as the thin film transistor provided in the liquid crystal panel. Accordingly, the writing speed is increased, compared with that in the related art, in addition to achievement of the advantages of increase in fineness and reduction in power consumption. As a result, an occurrence of the color shift is more effectively suppressed.

According to the ninth aspect of the present invention, use of indium gallium zinc oxide as the oxide semiconductor forming the channel layer reliably achieves advantages similar to those achieved in the eighth aspect of the present invention.

According to the tenth aspect of the present invention, advantages similar to those in the first aspect of the present invention are achieved in the method of driving the color-field sequential liquid crystal display apparatus.

Brief description of drawings

FIG. 1 is a block diagram illustrating the configuration of a data compensation circuit in a liquid crystal display apparatus according to a first embodiment of the present embodiment.

FIG. 2 is a waveform diagram for describing a method of acquiring a desired display luminance in a color-field sequential liquid crystal display apparatus.

FIG. 3 is a diagram for describing overdrive driving in the related art.

FIG. 4 is a diagram for describing the overdrive driving in the related art.

FIG. 5 is a diagram for describing the overdrive driving in the related art.

FIG. 6 includes waveform diagrams for describing data necessary to acquire an applied gradation value of a displayed field.

FIG. 7 includes waveform diagrams for describing data necessary to acquire a liquid-crystal state value at the end of a previous field.

FIG. 8 is a diagram for describing a data conversion process for determining the applied gradation value of the displayed field.

FIG. 9 is a diagram for describing a data conversion process for determining the applied gradation value of the displayed field.

FIG. 10 is a diagram for describing a data conversion process performed when data about an arbitrary displayed field is input.

FIG. 11 is a diagram for describing how to acquire the applied gradation value.

FIG. 12 is an exemplary gradation luminance table of red.

FIG. 13 is an exemplary gradation luminance table of green.

FIG. 14 is an exemplary gradation luminance table of blue.

FIG. 15 is a diagram for describing how to acquire the applied gradation value.

FIG. 16 is a diagram for describing an applied gradation value determination lookup table.

FIG. 17 is a diagram for describing the applied gradation value determination lookup table.

FIG. 18 includes diagrams for describing how to acquire the liquid-crystal state value.

FIG. 19 is a diagram for describing how to acquire the liquid-crystal state value.

FIG. 20 illustrates an exemplary liquid-crystal state value acquisition lookup table.

FIG. 21 is a block diagram illustrating the entire configuration of the liquid crystal display apparatus according to the first embodiment.

FIG. 22 illustrates the structure of one frame period in the first embodiment.

FIG. 23 is a diagram for describing the liquid-crystal state value acquisition lookup table in the first embodiment.

FIG. 24 is a diagram for describing the applied gradation value determination lookup table in the first embodiment.

FIG. 25 illustrates a principle of how color breakup occurs.

FIG. 26 illustrates the structure of one frame period in a second embodiment of the present invention.

FIG. 27 is a block diagram illustrating the entire configuration of a liquid crystal display apparatus according to the second embodiment.

FIG. 28 is a block diagram illustrating the configuration of a data compensation circuit in the second embodiment.

FIG. 29 is a diagram for describing local dimming.

FIG. 30 is a block diagram illustrating the entire configuration of a liquid crystal display apparatus according to a third embodiment of the present invention.

FIG. 31 is a block diagram illustrating the configuration of a data compensation circuit in the third embodiment.

FIG. 32 illustrates the structure of one frame period in a fourth embodiment of the present invention.

FIG. 33 is a block diagram illustrating the entire configuration of a liquid crystal display apparatus according to the fourth embodiment.

FIG. 34 is a block diagram illustrating the configuration of a data compensation circuit in the fourth embodiment.

FIG. 35 is a waveform diagram illustrating an example of how the liquid crystal state is varied when liquid crystal molecules have ideal response characteristics.

FIG. 36 is a waveform diagram illustrating an example of how the liquid crystal state is varied when the overdrive driving is not adopted.

FIG. 37 is a waveform diagram illustrating an example of how the liquid crystal state is varied when the overdrive driving is adopted. DESCRIPTION OF EMBODIMENTS 0. Introduction

The outline of the present invention will now be described with reference to FIG. 2 to FIG. 20 before embodiments are described. Liquid crystal display apparatuses capable of 256-gradation display are exemplified in the description here and the description of the embodiments.

<0.1 Concept of the Present Invention>

As described above, in a typical color-field sequential liquid crystal display apparatus, the liquid crystal state is varied also during the turning on of the backlight even if the transmittance reaches a target value in each field through the overdrive driving, thereby causing the color shift. Accordingly, as a method of achieving a desired display luminance in the color-field sequential liquid crystal display apparatus, control of an applied gradation value (a gradation value associated with the value of voltage to be actually applied to the liquid crystal) in each field so that the liquid crystal state is varied in a manner illustrated in a bold line 80 in FIG. 2 is proposed. Specifically, further enhancement of the temporal change of the values of data, compared with the overdrive driving, is proposed so that the integral value of the luminance values during the turning on of the backlight reaches a target display luminance. In the example illustrated in FIG. 2 , the RGB combination of an input gradation value (a target display gradation value) is “R=128, G=128, and B=32”, the RGB combination of a target attained gradation value is “R=183, G=105, and B=2”, and the RGB combination of the applied gradation value is “R=238, G=89, and B=0.”

In the overdrive driving in the related art, the applied gradation value of the displayed field is acquired on the basis of the input gradation value of the previous field (the first previous field of the displayed field) and the input gradation value of the displayed field. Specifically, as illustrated in FIG. 3 , the applied gradation value of the displayed field is acquired on the basis of the input gradation value of the previous field and the input gradation value of the displayed field using an arithmetic expression or a conversion table. In other words, the input gradation value of the displayed field is converted into the applied gradation value of the displayed field on the basis of the input gradation value of the previous field.

Here, for example, a first case and a second case will now be considered. In the first case, a color of an RGB combination of “R=128, G=128, and B=32” is to be displayed. In the second case, a color of an RGB combination of “R=128, G=128, and B=94” is to be displayed.

In the first case, the RGB combination of the target attained gradation value is “R=183, G=105, and B=2.” The RGB combination of the applied gradation value for realizing the target attained gradation value using the overdrive driving is “R=238, G=89, and B=0.” Accordingly, for example, in the case of the applied gradation value of the green field, as illustrated in FIG. 4 , the value “89” should be acquired on the basis of the input gradation value “128” of the red field and the input gradation value “128” of the green field using an arithmetic expression or a conversion table.

In the second case, the RGB combination of the target attained gradation value is “R=148, G=120, and B=84.” The RGB combination of the applied gradation value for realizing the RGB combination of the target attained gradation value using the overdrive driving is “R=168, G=112, and B=72.” Accordingly, in the case of the applied gradation value of the green field, as illustrated in FIG. 5 , the value “72” should be acquired on the basis of the input gradation value “128” of the red field and the input gradation value “128” of the green field using an arithmetic expression or a conversion table.

In the above examples, the values of the two pieces of data input into the arithmetic expression or the conversion table in the first case are equal to the values of the two pieces of data input into the arithmetic expression or the conversion table in the second case. However, the values of the pieces of data to be acquired in the first case are different from the values of the pieces of data to be acquired in the second case. This means that, “when only the arithmetic expression or the conversion table is used in the same manner as in the related art, it is not possible to acquire the applied gradation value at which the integral value of the luminance values during the turning on of the backlight reaches the target display luminance.”

Accordingly, in the present invention, the applied gradation value of each field is acquired through a data conversion process described below, which is different from that in the related art, so that the integral value of the luminance values during the turning on of the backlight reaches the target display luminance. The gradation value corresponding to the liquid crystal state (the state of orientation of liquid crystal molecules) at each time is hereinafter referred to as “a liquid-crystal state value.”

In acquisition of one target display luminance (the luminance corresponding to the input gradation value) in the displayed field (the current field), the target attained gradation value is varied depending on the liquid-crystal state value at the end of the previous field (the first previous field of the displayed field), as illustrated in FIG. 6 . In the example illustrated in FIG. 6 , the target attained gradation value of the displayed field when the liquid-crystal state value at the end of the previous field is relatively low is higher than that when the liquid-crystal state value at the end of the previous field is relatively high. The applied gradation value of the displayed field when the liquid-crystal state value at the end of the previous field is relatively low is also higher than that when the liquid-crystal state value at the end of the previous field is relatively high. Accordingly, the applied gradation value of the displayed field should be acquired on the basis of the input gradation value of the displayed field and the liquid-crystal state value at the end of the previous field. In other words, it is necessary to use the liquid-crystal state value at the end of the previous field, in addition to the input gradation value of the displayed field, as the data for determining the applied gradation value of the displayed field.

In terms of one target display luminance of the previous field, the liquid-crystal state value at the end of the previous field is varied depending on the liquid-crystal state value at the end of the second previous field of the displayed field, as illustrated in FIG. 7 . In the example illustrated in FIG. 7 , the liquid-crystal state value at the end of the previous field when the liquid-crystal state value at the end of the second previous field of the displayed field is relatively low is higher than that when the liquid-crystal state value at the end of the second previous field of the displayed field is relatively high. Accordingly, the liquid-crystal state value at the end of the previous field should be acquired on the basis of the input gradation value of the previous field and the liquid-crystal state value at the end of the second previous field of the displayed field. In other words, it is necessary to use the liquid-crystal state value at the end of the second previous field of the previous field, in addition to the input gradation value of the previous field, as the data for acquiring the liquid-crystal state value at the end of the previous field.

In consideration of the above facts, in the present invention, “a process of converting the input gradation value of the previous field into the liquid-crystal state value at the end of the previous field on the basis of the liquid-crystal state value at the end of the second previous field” and “a process of converting the input gradation value of the displayed field into the applied gradation value of the displayed field on the basis of the liquid-crystal state value at the end of the previous field” are performed as the data conversion process for determining the applied gradation value of the displayed field, as illustrated in FIG. 8 .

“The liquid-crystal state value at the end of the second previous field” in FIG. 8 is acquired by converting “the input gradation value of the second previous field” on the basis of “the liquid-crystal state value at the end of the third previous field.” As described above, the liquid-crystal state value at the end of each field is acquired in consideration of the liquid-crystal state values at the end of all the previous fields, as illustrated in FIG. 9 .

The liquid-crystal state value at the end of the displayed field is used for determining the applied gradation value of a field next to the displayed field. Accordingly, when data about an arbitrary displayed field is input, as illustrated in FIG. 10 , “a process of converting the input gradation value of the displayed field into the liquid-crystal state value at the end of the displayed field on the basis of the liquid-crystal state value at the end of the previous field” and “a process of converting the input gradation value of the displayed field into the applied gradation value of the displayed field on the basis of the liquid-crystal state value at the end of the previous field” are performed.

The description continues in the full USPTO document.